The invention relates to a glycol/boric acid/borate-based operating electrolyte for an aluminum electrolyte capacitor, which contains at least traces of water and an inhibitor that acts as an additive to reduce corrosion of the aluminum oxide coating of the capacitor.
An aluminum electrolyte capacitor contains two aluminum foils as electrodes, between which a separator impregnated with an operating electrolyte is arranged. An oxide coating is applied as a dielectric onto the aluminum foil serving as the anode. A paper is normally used as the separator. The operating electrolyte is selected in such a way as to ensure that it features adequate ion conductivity, adequate temperature stability at least across the operating temperature interval, electrolysis stability at its operating voltage and, in particular, chemical stability, so that decomposition processes taking place during operation of the electrolyte capacitor do not lead to gas exhalation that could jeopardize the tightness of the capacitor.
A number of ethylene glycol-based compounds for use in operating electrolytes are known from U.S. Pat. No. 4,469,610. The conductive salts used in these compounds include boric acid, ammonium borate, long-chain dicarboxylic acids, and salts of long-chain dicarboxylic acids. In known glycol/boric acid/borate-based operating electrolytes, problems occurs in electrolytes containing a high proportion of water. This water develops during esterification of the boric acid with the glycol. This water causes corrosion of dielectric aluminum oxide within the capacitor, especially at higher temperatures within the electrolyte capacitor. This corrosion damages the dielectric and results in gas development in the capacitor.